1. Field of the Invention
This invention relates to a process for desulfurization of coal, and more particularly relates to desulfurization of coal with extremely low amounts of microwave energy.
2. Description of the Prior Art
A large percentage of available raw coal in the United States contains around 1-5% of sulfur. For most industrial and private uses of coal, sulfur is an element which must be removed in order to utilize raw coal as a fuel for practical and beneficial applications. Desulfurized coal also has beneficial applications in a number of industries where, for example, corrosive combustion products are to be avoided and air pollution is to be minimized.
However, in general, practical method for desulfurization of coal are expensive and are inefficient. For instance, inefficiency results when coal is desulfurized by directly burning the coal in a non-critical area, such as at the mine mouth, in order to meet stringent government regulations concerning air pollution. Coal burned in this manner results in loss of volatiles which have great heating value. On the other hand, burning or heating coal in non-critical areas may result in costly heating and drying apparatus, as coal must be typically heated within temperature ranges of around 600.degree.-800.degree. C to release sulfur. Further, burning coal at the temperature ranges of around 600.degree.-800.degree. C, as in burning at the mine mouth, also results in loss of heating value due to the loss of volatiles.
In consequence of the above, more efficient processes are sought in order to make usable, in a practical sense, vast coal reserves in this country. For instance, prior art methods have suggested the following desulfurization processes: liberating sulfur at relatively low temperatures of about 300.degree.-400.degree. C by utilizing pressurized hydrogen; utilizing super heated steam in a temperature range of 150.degree.-300.degree. C; and utilizing both hot gases and microwave energy to heat coal at temperatures around 600.degree.-800.degree. C. Nevertheless, the above desulfurization processes executed within the stated temperature ranges have not satisfactorily decreased losses in heat value, or in sulfur production associated cost.
In addition to the above, others in the prior art have: generated high temperatures in a range of about 800.degree.-900.degree. C through inductive heating to liberate sulfur; washed coal with carbon disulfide, iron sulfate and chloride, and other organic solvents; scrubbed the combustion gases released by burning coal prior to releasing the combustion gases to the atmosphere; and separated sulfur from coal with magnetic fields. Likewise, these desulfurization processes have not heretofore proven commercially feasible.
For instance, washing coal with carbon disulfide necessitates the use of organic solvents which are expensive. Similarly, the process whereby coal is heated in the temperature range between 800.degree.-900.degree. C, as earlier noted, is costly and results in significant loss of the heating value of the coal. Lastly, liberating sulfur through the magnetic desulfurization process becomes difficult when the magnetic moment, developed by the particles to be separated, is not high enough for magnetic forces to overcome competing hydrodynamic gravitational forces.
Therefore, it is an object of this invention to provide an improved process for desulfurization of coal while still preserving the heating value of coal.
It is another object of this invention to provide an inexpensive yet efficient process for desulfurization of coal.